I got All the way up to 250K on a 2002 Chevy Suburban with a 5.3. Ran pretty problem free from when we acquired it at 79K. I ran Walmart brand synthetic oil most of the time, then for some unknown reason at the end before I sold it, I thought I’d try regular oil. That’s when it developed a stuck lifter. I did oil flushes and all sorts of things including returning to synthetic oil, but it continued to have a stuck lifter. Then my wife took a long trip from Colorado to Las Vegas and back, and it resolved. So, all in all I had very good luck with the 5.3, except for my bad decision to switch from synthetic oil.
i also had minimal issues with the auto trans, outside of fluid changes, again through to 250K miles.